Due to the availability of entire genomic DNA sequences in numerous organisms and the advance of recombinant DNA technology, it has become simple to clone any genes and subsequently overexpress them in prokaryotic or eukaryotic cells. The biochemical elucidation of protein functions requires obtaining proteins with high purity.
A number of approaches have been developed for the isolation and purification of proteins, particularly recombinant proteins, from other components of a biological sample. The approaches include ion exchange chromatography based on molecular charges, gel filtration based on molecular size, and affinity chromatography. The affinity chromatography is more specific and much more efficient than the other purification approaches because it makes use of the specific affinity of a protein for a purifying reagent such as an antibody or ligand to which it specifically binds. One member of a binding pair may be used to “tag” a protein of interest, with the other member used as an affinity ligand. Such a protein “tag” may be “fused” recombinantly and expressed to produce a fusion protein with the tag attached. The “tagged” fusion protein is then affinity purified by interaction with the binding partner of the tag and the tag is then optionally cleaved to release pure protein. However, the known affinity chromatography suffers from the drawbacks such as unsatisfactory purity, time-consuming, high cost and/or unusual elution conditions.